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Fragile X Syndrome

Abstract

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NORD is very grateful to Robert A. Saul, MD, Senior Clinical Geneticist, Training Program Director, Greenwood Genetic Center, for assistance in the preparation of this report.

Synonyms of Fragile X Syndrome

fragile site, folic acid type, rare, Fra(X)(Q27.3)

fragile X mental retardation protein, FMRP

fragile X mental retardation syndrome

marker X syndrome

Martin-Bell syndrome

mental retardation, X-linked, associated with Mar Xq28

X-linked mental retardation and macroorchidism

Disorder Subdivisions

No subdivisions found.

General Discussion

Fragile X syndrome is characterized by moderate intellectual disability in affected males and mild intellectual disability in affected females. Distinctive physical features are sometimes present in affected males including a large head, long face, prominent forehead and chin, protruding ears, loose joints and large testes, but these features develop over time and may not be obvious until puberty. Motor and language delays are usually present but also become more apparent over time. Behavioral abnormalities including autistic behaviors are common.

Fragile X syndrome is caused by an abnormality (mutation) in the FMR1 gene. Affected individuals have an increased number of copies of a portion of the gene called CGG repeats. The greater the number of copies of CGG, the more likely there will be increased severity of the disorder. Fragile X syndrome occurs more often in males and results in more severe disease in males.

Mutations in the FMR1 gene are associated with two other conditions in addition to the fragile X syndrome (FXTAS and POI) and these conditions have been termed FMR1-Related Disorders. (See the Related Disorders section of this report for brief summaries of the other disorders.)

Fragile X Syndrome Resources

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